In the operation of heavy telescopic variable boom length cranes, a substantial number of serious accidents occur through the hoisting of large weights and changing both the length and angle of the boom. As the angle subtended between the horizontal surface on which the crane rests and the boom is decreased, the moment of force exerted on the crane by the suspended weight increases, thereby increasing the tendency of the crane to tip over. As the boom length is increased, this tendency is similarly increased. Thus, a very real need exists for clear and accurate information regarding actual crane operating conditions. This information must be quickly and accurately provided to the crane operator, which will improve his ability to operate the crane safely. Such information must be calculated from data based on the geometrical configuration of the particular crane in use, as well as on the relative weight of the load, boom angle and length existing at the time the desired information is provided.
Of primary interest to the crane operator for safe operation of the crane is an indication of the percent of safe load at which the crane is operating. As the boom moves upwardly and downwardly in handling each load, the percent safe load changes accordingly and instant calculation is required which is continuous as the crane operates.
Various safety factors are required by legal regulations for the cable, boom, and sheaves used in crane hoist apparatus. Also, visual and audible warnings are necessary to assist the operator operating the crane within the design limits established by the crane manufacturer. The crane operator needs accurate and continuous information relating to the vital conditions affecting safe crane operation, before safe limits are exceeded, i.e., before such warnings actually go into operation, or as the unsafe conditions bringing about such warnings are approached. The geometry of the crane configuration requires automatic trigonometric calculations for the percent safe load and load radius, which are varying functions of the boom angle and length, and which may vary as the load is handled. Also, the parameter configuration data for such calculations must always be taken into consideration in the processing thereof for each crane, and this varies with different crane manufacturers' specifications.
Thus, the desired information must be based on data which conforms to the configuration of the crane in use. It is desirable to provide a modular system which can be adapted for use with any desired one of a plurality of different presently available crane configurations. In accordance with the present invention, this is accomplished by a universally applicable system which can be equipped with selectable memory circuits such that the system is programmed to handle the configuration of any variable boom length type crane that is presently on the market.
There is also at present great need for a universal system having modular units that can be made in production, with each suitable for use with any known variable boom length type of crane. This is accomplished by the present system which comprises, in addition to several sensors, a programmable logic and control unit, and at least one display unit, each of which is easily mounted on the crane at appropriate locations.
The use and handling of as few analog components as possible is also highly desirable in systems that are exposed to severe weather and operating conditions, since they are subject to error and drifting due to temperature variations and age. The maximum use of digital type equipment is a feature of the present invention, along with the use of a minimal amount of analog equipment, as only the boom angle, length, load and percent safe load indicator units use analog signal circuits.